1. Field
The present invention relates to a lighting device and, more particularly, to a lighting device capable of changing a serial/parallel connection structure of light-emitting elements based on an input voltage.
2. Description of the Related Art
A light-emitting diode (LED) refers a type of semiconductor element capable of implementing light of various colors by forming a light-emitting source using a PN diode of a compound semiconductor. The LED has a long life, a small size, and a small weight, and can be driven using a low voltage. In addition, the LED is durable against impact and vibration, does not require preheating or complicated driving, and is mountable on a substrate or a lead frame in various forms before packaging. As such, the LED may be modularized for various purposes and applied to a backlight unit or a variety of lighting devices.
A plurality of LEDs may be used to provide an independent lighting device. In this case, the LEDs may be connected to each other in series or in parallel. In this case, commercial power may be converted into alternating current (AC) power and the AC power may be provided to the LEDs to always turn on all LEDs.
When the AC power is provided and used as described above, an AC rectifier is necessary. However, the AC power may be directly applied to the LEDs without using the AC rectifier. In this case, the LEDs may be connected to each other in series, and on/off states of the LEDs may be changed based on the magnitude of a variable input voltage. As the on/off states are repeated, flicker of light occurs, usability of each LED is reduced, and thus light output efficiency is reduced.